When people reach their 40s, muscle mass and strength begin to decline, and up to 50% of muscle mass is lost by the time people reach their 80s. This decline leads to sarcopenia, a syndrome of progressive loss of muscle and strength that is a leading cause for reduced function and loss of independence in aged adults. With an aging global population, scientists want to find therapeutic options to mitigate age-related sarcopenia.

With treating this syndrome in mind, Sen and colleagues from the Indiana University School of Medicine recently published a study in Scientific Reports on the effects of a compound used in ancient Indian medicine called urolithin A on aged muscle. They found that giving mice oral doses of urolithin A improved cellular levels of an essential molecule called nicotinamide adenine dinucleotide (NAD+), improved cellular energy production, and activated the generation of blood vessels in muscle. “This work lays the foundation to future work testing the effect of [urolithin A] supplementation on sarcopenia and its outcomes,” stated Sen and colleagues in their publication.

Urolithin A is a nutritional supplement abundant in Shilajit, a sticky substance found in rocks of the Himalayas. Shilajit develops from the slow decomposition of plants over centuries and is used in traditional Ayurvedic medicine, one of the world’s oldest medical healing systems developed more than 3,000 years ago in India. Studies have indicated that this substance may have various health benefits during aging from boosting testosterone levels in men to improving muscle function. “In this work, we sought to understand the mechanism of action of orally supplemented [urolithin A] on limb skeletal muscles,” said Sen and colleagues in their publication.

They found that urolithin A supplementation in mice delayed the onset of muscular aging. The scientists began treating the mice orally with a solution of 10 mg/kg urolithin A starting at 12 weeks of age and continued treating them for 16 weeks. At age 28 weeks, the mice were the equivalent age of a human between 35 and 40 years old. Compared to 28 week old mice not given urolithin A, the mice supplemented with urolithin A had significantly reduced levels of molecular markers of aging in their muscles, which suggested delayed aging.

Since urolithin A supplementation blunted the levels of molecular markers of aging in muscle, Sen and colleagues looked at the effects of urolithin A on energy production in aged muscle. They found urolithin A increased levels of the cellular energy molecule adenosine triphosphate (ATP) and a molecule vital for energy production, NAD+. They found that the increased NAD+ levels from urolithin A supplementation were comparable to the effects of supplementing with five-fold higher doses of NAD+ precursor nicotinamide riboside (NR). 

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(Ghosh et al., 2020 | Scientific Reports) Urolithin A supplementation increased ATP and NAD+ levels in aged muscle. Figure A shows the hindlimb region of the mouse where the team performed their analysis of ATP and NAD+ levels. Figure C shows a significant increase in molecules used for energy in cells called adenosine triphosphate (ATP) after 16 weeks of urolithin A supplementation. Figure D illustrates a significant increase in cellular NAD+ levels following the 10 mg/kg dose of urolithin A supplementations. Figure B indicates significantly increased levels of NAD+ following 50 mg/kg supplementations with NAD+ precursor nicotinamide riboside (NR).

To look into the molecular mechanisms behind the action of urolithin A in muscle, Sen and colleagues performed a genetic analysis to find out what pathways become activated in muscle by urolithin A. Their results pointed to higher levels of gene activity in pathways that generate blood vessels.

(Ghosh et al., 2020 | Scientific Reports) Urolithin A supplementation for 12 weeks increased expression of blood vessel generating genes in mouse muscle cells. Each graph represents the levels of genes involved in blood vessel formation in muscle. Following 12 weeks of urolithin A supplementation, the levels increased significantly for these genes. This indicates that urolithin A can stimulate blood vessel formation in muscles.

The team of scientists then found evidence that the urolithin A-induced increased generation of muscle blood vessels occurs via sirtuin 1. This protein, known for its anti-aging role,  activates other proteins by removing molecular tags called acetyl groups. The team’s analyses showed increased levels of sirtuin 1 upon urolithin A supplementation. When the scientists treated muscle cells with a combination of urolithin A and an inhibitor of sirtuin 1 called selisistat EX527, they found a reduction in molecular indicators of blood vessel formation. These results indicated that urolithin A stimulates muscle blood vessel formation via a sirtuin-dependent mechanism.

(Ghosh et al., 2020 | Scientific Reports) Supplementation with urolithin A increases blood vessel formation in muscle via a sirtuin 1-dependent cellular mechanism. In In the boxes, the green stain labels the markers VEGFR2 and VEGFA in blood vessel formation. The blue stain labels DNA, which indicates the center of cells (nuclei). Urolithin A increases the presence of the green stain for both markers of blood vessel formation, and EX527, the sirtuin 1 inhibitor, decreases the blood vessel formation. Both graphs represent the levels of markers for blood vessel formation. In both cases, urolithin A supplementation increased the levels of the markers VEGFR2 (top) and VEGFA (bottom), indicating increased blood vessel formation in muscle. The combined administration of the sirtuin 1 inhibitor EX527 with urolithin A blunted the levels of these blood vessel formation markers. This means that urolithin A stimulates blood vessel formation via a sirtuin 1-dependent mechanism.

Blood vessel formation in muscle is a key determinant of muscular and overall physical function. Urolithin A supplementation significantly blunted markers of aging, improved cellular energy production, and stimulated blood vessel formation in the muscle of aged mice. If urolithin A can induce these same effects in humans, this could be used therapeutically to combat age-related sarcopenia.

“This work provides maiden evidence demonstrating that urolithin A supplementation bolsters skeletal muscle ATP and NAD+ levels causing upregulated angiogenic pathways,” said Sen and colleagues in their publication. Future work will likely entail human clinical trials to show whether the promising effects of urolithin A in rodents occur in people as well. If so, the supplement could provide a means to combat age-related sarcopenia.